UNITED NATIONS (AP) ' The U.N. peacekeeping chief says there are strong suspicions that fighters supporting the Syrian regime were responsible for some of the 108 killings in the Houla area last week along with heavy weapons fired illegally by the government.

Herve Ladsous told reporters Tuesday that he has seen no reason to believe that "third elements" ' outside forces ' were involved in one of the bloodiest single events of Syria's 15-month-old uprising, though he did not rule it out.

The Syrian government has denied any responsibility for the massacre and is blaming "armed terrorists."

Ladsous said the presence of U.N. observers is saving lives. But he said their armored vehicles are being shot at regularly, including on Tuesday. He blamed the government and opposition.